Medical procedures are known for treating various injuries or conditions where structures are attached to bones for treatment of the injury or condition. Various apparatus and methods are known for surgically treating various spinal problems wherein structures are attached to the spine. Spinal fixation procedures treat the spine by attaching devices to the spine to facilitate fixation of specified vertebrae of the spine. For example, U.S. Pat. No. 4,653,481, issued Mar. 31, 1987 to Howland et al., concerns spine fixation systems and methods. U.S. Pat. No. 5,030,220, issued Jul. 9, 1991 to Howland, concerns alternative spine fixation systems and methods. U.S. Pat. Nos. 4,653,481 and 5,030,220 are incorporated herein by reference.
U.S. Pat. Nos. 4,653,481 and 5,030,220 both relate to systems and methods which employ spine fixation devices including a plurality of clamp assemblies. Each clamp assembly is threadably attached to a vertebra of the spine. Connecting structure, such as a rod, is held by each of the clamp assemblies to connect the vertebra to facilitate fixation of the spine.
With respect to attaching spine fixation devices to the spine, a significant concern is the ability to securely attach the fixation devices to the individual vertebra. One problem encountered when attaching devices to bones such as the bony structure of vertebrae is that the vertebrae typically have irregular outer surfaces. Also, vertebrae are relatively small bones with a plurality of small and irregular projecting members, which may easily be fractured. Further, problems are presented due to the structure and composition of each vertebra. An outer portion of each vertebra usually includes relatively hard and strong cortical bone. An interior portion of each vertebra usually includes softer and weaker cancellous bone.
A need exists in the prior art for systems and methods which permit secure attachment of spine fixation devices or other devices to bones and which address at least some or all of the various concerns noted above and other concerns.